Remove temporary external url for thumbnail on virtual immersive video tours

In https://github.com/artshumrc/giza/pull/147 remove one of the external URLs used during development

This URL:
https://github.com/artshumrc/giza/pull/147/commits/f617512cb84432d8140c8f8d585bae48b452eab5#diff-ec9b3e76fb65b0b1a9deb3796c8b1d5176ea74729099fc1b64861dc034271d01L11